Core Shell Silica Particles and Uses Thereof As an Anti-Bacterial Agent

ABSTRACT

This invention provides core shell silica particles, wherein each core shell silica particle comprises a silica core, and a surface of the silica core etched with group I metal silicate. These core shell silica particles have high surface charge density and anti-bacterial activity. Also provided are compositions comprising core shell silica particles, process of making the core shell silica particles and methods of reducing or inhibiting bacterial activity by administering the core shell silica particles or compositions thereof.

BACKGROUND

Silica (SiO₂) particles are commonly used as abrasive and/or thickenersin oral care compositions usually in the form of fumed silica orprecipitated silica. One of the benefits of using silica is their lowcost. However, silica has limited utility besides its abrasive and/orthickening effect. As a result, other active agents must be added to anoral care composition to provide a desired effect (e.g., adding ananti-bacterial agent to provide an anti-bacterial effect, addingtartar-control agents for tartar control). The need to add other activeagents not only raises the possibility that the oral care compositionwill not meet regulatory burdens which can arise when the other activeagents are used, but also increases the possibility that the oral carecomposition will not be desirable to the user of the composition (e.g.user sensitivity to the surfactant sodium lauryl sulfate (SLS), useraversion to the taste of a zinc compound, salty flavor andcrystallization issues with current tartar-control agents etc.).Moreover, further problems may arise. For example, a common problem withthe use of an anti-bacterial agent is the development of resistance bybacteria to the agent.

Core-shell structured colloidal particles have been known for severaldecades. The most famous example is the light-diffracting precious Opalwhich is formed slowly in several thousand years in naturalenvironments. Its core-shell structures were discovered by electronmicroscope in 1960s. Various synthetic core-shell colloidal particleshave been made since then. However, the synthesis of such core-shellmaterials is often complex, requiring multistep coating methodologies(See Kalele et al, “Nanoshell particles: synthesis, properties andapplications”, current science, vol. 91, no. 8, 25 Oct. 2006). Thereforealthough the core-shell technology has been known for several decades,it has not yet been applied in the dentifrice industry, probably due tothe high cost of making the CSS abrasive materials.

Therefore, there is still a need in the art for oral care compositionswith multifunctional effects, but with a minimum of ingredientsnecessary to achieve the multifunctional effects. There is also still aneed to develop additional anti-bacterial agents and tartar controlagents suitable for use in oral care compositions.

BRIEF SUMMARY

The present invention relates to core shell silica particles, whereineach core shell silica particle comprises a silica core, and a surfaceof the silica core etched with group I metal silicate.

The present invention also relates to compositions comprising the coreshell silica particles.

The present invention also relates to the process for making the coreshell particles which comprises admixing an amount of silica particlesin water with an amount of base, wherein the base comprises a group Imetal ion, to produce the core shell silica particles.

The present invention also relates to a method for reducing orinhibiting bacteria in the oral cavity of a patient in need thereof,which comprises applying to the oral surfaces of the patient thecomposition of the invention.

Reference to metal CSS particles refer to the metal with the appropriate+1 charge, e.g. for Na-CSS, the Na is Na+, for K-CSS, the K is K+, etc.

As used throughout, ranges are used as shorthand for describing each andevery value that is within the range, and for describing sub-rangeswithin the range. Any value within the range can be selected as theupper terminus of the sub-range. Any value within the range can beselected as the lower terminus of the sub-range.

In addition, all references, books, patents, and patent applicationpublications cited herein are hereby incorporated by reference in theirentireties. In the event of a conflict in a definition in the presentdisclosure and that of a cited reference, book, patent, or patentapplication publication, the present disclosure controls.

Unless otherwise specified, reference to ambient or room temperaturerefers to a temperature range of 20-25° C.

Unless otherwise specified, all percentages and amounts expressed hereinand elsewhere in the specification should be understood to refer topercentages by weight based on the total weight of the composition.

The phrase “and/or” as used herein, with option A and/or option B forexample, encompasses the individual embodiments of (i) option A; (ii)option B; and (iii) option A plus option B.

It is understood that wherever embodiments are described herein with thelanguage “comprising,” otherwise analogous embodiments described interms of “consisting of” and/or “consisting essentially of” are alsoprovided.

Where aspects or embodiments of the invention are described in terms ofa Markush group or other grouping of alternatives, the present inventionencompasses not only the entire group listed as a whole, but each memberof the group and all possible subgroups of the main group, but also themain group absent one or more of the group members. The presentinvention also envisages the explicit exclusion of one or more of any ofthe group members in the claimed invention.

All combinations of the various elements described herein are within thescope of the invention unless otherwise indicated herein or otherwiseclearly contradicted by context.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of a core shell silica particle of theinvention.

FIG. 2 shows a schematic of the core shell silica particle showingparameters defined in the light scattering model described in paragraph[0141] below.

FIG. 3 shows a schematic of a core shell silica particle of theinvention wherein an internal surface of the silica core is etched withmetal silicate.

DETAILED DESCRIPTION

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Description of the Core Shell Silica Particles

The present invention provides core shell silica particles, wherein eachcore shell silica particle comprises a silica core, and a surface of thesilica core etched with group I metal silicate.

Core shell silica particles are prepared by etching silica (SiO₂) with abase to form core(Silica)-shell(metal silicate) structured colloids. Forexample using NaOH as the base, core(SiO₂)-shell(Na₂SiO₃) structuredcolloids are formed. The reaction is as follows:

The Na₂SiO₃ molecules (contributing 2 negative charges with 2 Na+counter ions) on colloidal core-shell silica particle surface.

A surface of the silica core is etched with metal silicate. The term“etched” means that a surface of the silica core is dissolved, and groupI metal silicate is formed on top of the silica core. The process formaking the core shell silica (CSS) particles of the invention comprisesetching the original silica in order to form the Na₂SiO₃. The reactionof the silica particle with base causes a reduction in the diameter ofthe silica particle to form a silica core, and group I metal silicate isformed on top of the silica core. The Na₂SiO₃ layers are not additionallayers coated on top of the original surface of the silica.

Methods of forming particles by coating silica with silicate aredescribed in the prior art (e.g. Kalele et al, “Nanoshell particles:synthesis, properties and applications”, current science, vol. 91, no.8, 25 Oct. 2006). However, these methods of preparing silica/silicateparticles are more complex, costly and different than etching themethods described in the present application.

The metal silicate typically comprises the formula M₂SiO₃.x H₂O, whereinM is a group I metal, and x is from 0 to 10. The metal silicate may beanhydrous, i.e. x=0, or may be hydrated. Preferably, M is Na or K.

The surface of the silica core may be the outer surface of the silicacore (see FIG. 1A).

Alternatively, or in addition, the surface of the silica core may be aninternal surface of the silica core (see FIG. 2).

In one embodiment the outer 10 nm depth of each particle comprises from0.1 to 10, optionally 0.1 to 2 weight % M₂SiO₃.xH₂O.

In one embodiment the outer 10 nm depth of each particle has the generalformula:

SiO₂)_(p)[O_(o)*M⁺ _(m)H⁺ _(h)OH⁻ _(j)].qH₂O

wherein O* is oxygen in the silicate form; M is a group I metal ion; p,o, m, h, j and q are the atomic percentages of each component (p is theatomic percentage of SiO₂, O is the atomic percentage of oxygen in thesilicate form, m is the atomic percentage of group I metal, h is theatomic percentage of H⁺, j is the atomic percentage of OFF, and q is theatomic percentage of H₂O); and the total charge of each core shellsilica particle is zero.

Typically the atomic percentage for each component except H+ isdetermined by electron spectroscopy for chemical analysis (ESCA).

Optionally, the outer 10 nm depth of each particle has one of thefollowing compositions:

(SiO₂)_(30.30)Na_(0.41).8.70H₂O

(SiO₂)_(30.67)Na_(0.36).7.63H₂O

(SiO₂)_(23.25)[O*_(11.73)H_(10.26)Na_(13.20)].5.33H₂O

The d(0.5) or d50 of the particles is the diameter (typically inmicrons) that splits the distribution with half the population above andhalf below this diameter. It will be noted that this parameter is avalue for a population of particles, and that the diameter of anindividual particle may be larger or smaller than the d(0.5) valuesdescribed herein. The Dv50 (or Dv0.5) is the median for a volumedistribution, Dn50 is used for number distributions, and Ds50 is usedfor surface distributions. In the present context, d(0.5) will be usedto refer to the median particle size for a volume distribution.

In one embodiment, the d(0.5) value of the CSS particles is from 5 nm to50 μm.

In another embodiment, the d(0.5) value of the CSS particles may be from26 μm to 40 μm. Particles having a d(0.5) value within this range aretypically translucent. Translucent particles are those which allow lightto pass through, although it is not possible to see an image through theparticles. This is distinguished from transparent compositions whichallow light to pass through and an image can be seen through thecomposition. Methods for determine particle size are well known in theart. For example particle size may be determined using light scatteringmethodologies, such as using the Mastersizer 2000, Hydro 2000S, MalvernInstruments Limited.

In another embodiment, the d(0.5) value of the CSS particles may be from18 μm to 25 μm. Particles having a d(0.5) value within this range aretypically semi-opaque.

In another embodiment, the d(0.5) value of the CSS particles may be from10 μm to 15 μm. Particles having a d(0.5) value within this range aretypically opaque.

In another embodiment, the d(0.5) value of the CSS particles may be from5 μm to 15 μm.

In another embodiment, the d(0.5) value of the CSS particles may be from2.5 μm to 4.5 μm.

In another embodiment, the d(0.5) value of the CSS particles may be from5 nm to 20 nm.

In another embodiment, the d(0.5) value of the CSS particles may be from10 nm to 15 nm.

The d(0.1) value of the CSS particles is the diameter that splits thedistribution with 10% of the population below and 90% above thisdiameter.

The d(0.9) value of the CSS particles is the diameter that splits thedistribution with 90% of the population below and 10% above thisdiameter.

A value used to describe the distribution width of the particle sizedistribution is the span:

Span=(d(0.9)−d(0.1))/d(0.5)

The span of the core shell silica particles according to the presentinvention is typically from 1.5 to 3.

In a preferred embodiment, the CSS have a d(0.1) of from 10 to 13 μm, ad(0.5) of from 30 to 33 μm, and a d(0.9) of from 61 to 64 μm.

In another preferred embodiment, the CSS have a d(0.1) of from 6 to 9μm, a d(0.5) of from 18 to 21 μm, and a d(0.9) of from 41 to 45 μm.

In a further preferred embodiment, the CSS have a d(0.1) of from 3 to 5μm, a d(0.5) of from 11 to 14 μm, and a d(0.9) of from 33 to 36 μm.

In preferred embodiments, the d(0.5) value of the CSS particles is lessthan the mean diameter of a human dentin tubule. This allows the CSSparticles to enter the dentin tubules, which may be exposed on damage tothe protective enamel layer. In human teeth, dentin tubule mean diameternear the dentino-enamel junction is 0.9 μm, the middle section of thedentin tubule has a diameter of about 1.2 μm and near the pulp thediameter is about 2.5 μm.

In another embodiment of the invention, a silica source is selected toproduce CSS particles which fits into the dentin tubule (e.g. Aerosil®200—a fumed silica (synthetic amorphous silica) with a d(0.5) of 0.012μm). In another embodiment of the invention, the d(0.5) value of the CSSparticles is less than 0.9 μm. In still another embodiment of theinvention, the CSS particle has a d(0.5) in the range of 0.010 μm—lessthan 0.9 μm. In another embodiment of the invention, the CSS particlesof the invention can also plug, block holes in the enamel.

CSS particles may be spherical, or substantially spherical however itwill be understood that the particles may have other shapes, for examplerod, needle, or ellipsoidal shapes. The particles may have irregularshapes. The particles may also form larger size aggregates.

The M₂SiO₃.xH₂O may comprise a plurality of monolayers of M₂SiO₃.xH₂O.The number of monolayers may be from 2 to 100, from 2 to 40, 2 to 12 or12 to 40 monolayers.

The particle may comprise 2, 4, 16, 32 or 36 surface M₂SiO₃.xH₂Omonolayers.

The silica is preferably selected from the group consisting of aprecipitated silica, a fumed silica and a fused silica.

Core shell silica particles preferably have a high surface chargedensity and ion exchange capacity. Optionally, the core shell silicaparticles have a total cationic exchange capacity of from 0.5 to 5.0meq/g.

In one embodiment, the core shell silica particles have a turbidity offrom 0.0 to 0.2 at a wavelength of from 300 to 800 nm using a 0.20 mmquartz UV optical cell. These particles may be described as translucentor transparent.

In another embodiment, the core shell silica particles have a turbidityof from 0.8 to 1.6 at a wavelength of from 300 to 800 nm using a 0.20 mmquartz UV optical cell. These particles may be described as semi-opaque.

In a further embodiment, the core shell silica particles have aturbidity of from 1.8 to 2.4 at a wavelength of from 300 to 800 nm usinga 0.20 mm quartz UV optical cell. These particles may be described asopaque.

In a further aspect, the present invention provides a compositioncomprising the core shell silica particles described above.

The composition may be a powder abrasive. This composition does notcomprise a humectant.

The composition may comprise the core shell silica particles definedabove and a carrier.

Preferably, the composition is an oral care composition and furthercomprises an orally acceptable carrier.

The oral care composition is in form of a solid, paste, gel compositionor liquid composition. The composition may take any dosage form usefulfor oral administration. Illustrative examples of these include, but arenot limited to, a dentifrice, e.g., a toothpaste, dental gel, dentalcream, or tooth powder; a mouthwash, mouth rinse, or mouth spray; anoral slurry or liquid dentifrice; a gum or other confectionary; alozenge; dental floss or dental tape; a prophylaxis paste or powder; amono- or multi-layer oral film or gel strip, e.g., tooth strips orbreath strips, preferably using a biodegradable or orally consumablefilm or gel; functional film or gel flakes or functional micro-, ornano-particles; a film-forming composition comprising pre-gel(s) orpre-polymer(s), e.g., film-forming dentifrices, dental paints; a toothhardener; or a coating on an oral, e.g., orthodontic, appliance orimplant.

The orally acceptable carrier is preferably water.

For solid dentifrices such as toothpastes, the amount of water in thecomposition is selected from an amount consisting of less than 10% byweight, less than 5% by weight, less than 1% by weight. In each of theseamounts, the lower range for the amount of water is 0% or no more than0.1% water.

The orally acceptable carrier may further comprise a humectant. Thehumectant may be ethanol, a polyhydric alcohol, which includes, but isnot limited to glycerin, glycol, inositol, maltitol, mannitol, sorbitol,xylitol, propylene glycol, polypropylene glycol (PPG), polyethyleneglycol (PEG) and mixtures thereof, and a saccharide, which includes, butis not limited to fructose, glucose, sucrose and mixtures of saccharides(e.g. honey).

In an embodiment of the composition, the core shell silica particles arepresent in an amount of from 0.1 wt % to 35 wt %, based on the weight ofthe composition. In another embodiment of the composition, the CSSparticles are present in an amount from 0.1% to 1%. In anotherembodiment of the composition, the CSS particles are present in anamount from 0.5% wt. % to 20 wt. %, In another embodiment of thecomposition, the CSS particles are present in an amount from 1% wt. % to10 wt. %.

In an embodiment of the composition comprising a carrier, the refractiveindex of the core shell silica particles is within ±0.1 units of therefractive index of the carrier.

The carrier may include, but is not limited to water or other aqueoussolvent systems.

The oral care composition may further comprise an anti-bacterial agent.Possible anti-bacterial agents include, but are not limited to triclosan(5-chloro-2-(2,4-dichlorophenoxy)phenol); 8-hydroxyquinoline and saltsthereof, zinc and stannous ion sources such as zinc citrate, zincsulphate, zinc glycinate, sodium zinc citrate and stannouspyrophosphate; copper (II) compounds such as copper (II) chloride,fluoride, sulfate and hydroxide; phthalic acid and salts thereof such asmagnesium monopotassium phthalate; sanguinarine; quaternary ammoniumcompounds, such as alkylpyridinium chlorides (e.g., cetylpyridiniumchloride (CPC), combinations of CPC with zinc and/or enzymes,tetradecylpyridinium chloride, and N-tetradecyl-4-ethylpyridiniumchloride); bisguanides, such as chlorhexidine digluconate, hexetidine,octenidine, alexidine; halogenated bisphenolic compounds, such as 2,2′methylenebis-(4-chloro-6-bromophenol); benzalkonium chloride;salicylanilide, domiphen bromide; iodine; sulfonamides; bisbiguanides;phenolics; piperidino derivatives such as delmopinol and octapinol;magnolia extract; thymol; eugenol; menthol; geraniol; carvacrol; citral;eucalyptol; catechol; 4-allylcatechol; hexyl resorcinol; methylsalicylate; antibiotics such as augmentin, amoxicillin, tetracycline,doxycycline, minocycline, metronidazole, neomycin, kanamycin andclindamycin; and mixtures thereof.

A further illustrative list of useful antibacterial agents is providedin U.S. Pat. No. 5,776,435, which is incorporated herein by reference. Afurther illustrative list of zinc ion sources include, but is notlimited to the zinc salts include, but are not limited to zinc acetate,zinc borate, zinc butyrate, zinc carbonate, zinc chloride, zinc citrate,zinc formate, zinc gluconate, zinc glycerate, zinc glycolate, zinclactate, zinc oxide, zinc phosphate, zinc picolinate, zinc proprionate,zinc salicylate, zinc silicate, zinc stearate, zinc tartrate, zincundecylenate and mixtures thereof.

In some embodiments, the anti-bacterial agent is present at aconcentration selected from the group consisting of from 0.001% to 3%,by weight, 0.05% to 2%, by weight and 0.075% to 1.5% by weight.

In one embodiment there is no additional anti-bacterial agent except forthe core shell silica particles of the invention.

The composition may further include anti-caries agents, desensitizingagents, viscosity modifiers, diluents, surfactants, emulsifiers, foammodulators, pH modifying agents, abrasives, mouth feel agents,sweetening agents, flavor agents, colorants, preservatives, amino acids,anti-oxidants, anti-calculus agents, a source of fluoride ions,thickeners, an active agent for prevention or treatment of a conditionor disorder of hard or soft tissue of the oral cavity, and adhesiveagent, a whitening agent and combinations thereof.

It is understood that while general attributes of each of the abovecategories of materials may differ, there may be some common attributesand any given material may serve multiple purposes within two or more ofsuch categories of materials. Preferably, the carrier is selected forcompatibility with other ingredients of the composition.

An embodiment of the composition optionally comprises an amino acid.Suitable amino acids include, but are not limited to arginine, cysteine,leucine, isoleucine, lysine, alanine, asparagine, aspartate,phenylalanine, glutamate, glutamic acid, threonine, glutamine,tryptophan, glycine, valine, praline, serine, tyrosine, and histidine,and a combination of two or more thereof. The amino acids can include R-and L-forms and salt forms thereof. The amino acids (and salt formsthereof) can also include acid ester and/or fatty amide derivatives ofthe amino acid (e.g. ethyl lauroyl arginate hydrochloride (ELAH)).

An embodiment of the composition optionally comprises an antioxidant.Any orally acceptable antioxidant can be used, including butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), vitamin A,carotenoids, vitamin E, flavonoids, polyphenols, ascorbic acid, herbalantioxidants, chlorophyll, melatonin, and mixtures thereof.

An embodiment of the composition optionally comprises an anticalculus(tartar control) agent. Suitable anticalculus agents include withoutlimitation phosphates and polyphosphates (for example pyrophosphates),polyaminopropanesulfonic acid (AMPS), hexametaphosphate salts, zinccitrate trihydrate, polypeptides, polyolefin sulfonates, polyolefinphosphates, diphosphonates. The anticalculus agent is present at about0.1% to about 30%. The oral composition may include a mixture ofdifferent anticalculus agents. In one preferred embodiment, tetrasodiumpyrophosphate (TSPP) and sodium tripolyphosphate (STPP) are used. Theanticalculus agent comprises TSPP at about 1-2% and STPP at about 7% toabout 10%.

An embodiment of the composition optionally comprises at least oneorally acceptable source of fluoride ions. Any known or to be developedin the art may be used. Suitable sources of fluoride ions includefluoride, stannous fluoride, sodium fluoride, potassium fluoride, aminefluoride, ammonium fluoride, stannous monofluorophosphate, sodiummonofluorophosphate, potassium monofluorophosphate, aminemonofluorophosphate, ammonium monofluorophosphate, stannousfluorosilicate, sodium fluorosilicate, potassium fluorosilicate, aminefluorosilicate ammonium fluorosilicate, and mixtures thereof. One ormore fluoride ion-releasing compound is optionally present in an amountproviding a total of about 100 to about 20,000 ppm, about 200 to about5,000 ppm, or about 500 to about 2,500 ppm, fluoride ions.

An embodiment of the composition optionally comprises various dentifriceingredients to adjust the rheology and feel of the composition such assurface active agents, thickening or gelling agents, etc.

An embodiment of the composition optionally comprises a stannous ion ora stannous ion source. Suitable stannous ion sources include withoutlimitation stannous fluoride, other stannous halides such as stannouschloride dihydrate, stannous pyrophosphate, organic stannous carboxylatesalts such as stannous formate, acetate, gluconate, lactate, tartrate,oxalate, malonate and citrate, stannous ethylene glyoxide and the like.One or more stannous ion sources are optionally and illustrativelypresent in a total amount of about 0.01% to about 10%, for example about0.1% to about 7% or about 1% to about 5%.

An embodiment of the composition optionally comprises a surface activeagent (surfactant). Suitable surfactants include without limitationwater-soluble salts of C₈-C₂₀ alkyl sulfates, sulfonated monoglyceridesof C₈-C₂₀ fatty acids, sarcosinates, taurates, sodium lauryl sulfate,sodium cocoyl monoglyceride sulfonate, sodium lauryl sarcosinate, sodiumlauryl isoethionate, sodium laureth carboxylate and sodium dodecylbenzenesulfonate, and cocoamidopropyl betaine.

An embodiment of the composition optionally comprises a thickener. Anyorally acceptable thickening agent can be used, including withoutlimitation carbomers, also known as carboxyvinyl polymers, carrageenans,also known as Irish moss and more particularly—carrageenan(iota-carrageenan), high molecular weight polyethylene glycols (such asCarbowax®, available from The Dow Chemical Company), cellulosic polymerssuch as hydroxyethylcellulose, carboxymethylcellulose (CMC) and saltsthereof, e.g., CMC sodium, natural gums such as karaya, xanthan, gumarabic and tragacanth, colloidal magnesium aluminum silicate, andcolloidal and/or fumed silica and mixtures of the same. One or morethickening agents are optionally present in a total amount of about 0.1%to about 90%, for example about 1% to about 50% or about 5% to about35%.

An embodiment of the composition optionally comprises flavorants,sweeteners, colorants, foam modulators, mouth-feel agents and othersadditively may be included if desired, in the composition.

An embodiment of the composition optionally comprises one or morefurther active material(s), which is operable for the prevention ortreatment of a condition or disorder of hard or soft tissue of the oralcavity, the prevention or treatment of a physiological disorder orcondition, or to provide a cosmetic benefit. Examples of such furtheractive ingredient comprise a sialagogue or saliva-stimulating agent, anantiplaque agent, an anti-inflammatory agent, and/or a desensitizingagent.

Adhesion enhancing agents can also be added to the oral carecompositions which include but is not limited to waxes, inclusive ofbees' wax, mineral oil, plastigel, (a blend of mineral oil andpolyethylene), petrolatum, white petrolatum, shellac, versagel (blend ofliquid paraffin, butene/ethylene/styrene hydrogenated copolymer)polyethylene waxes, microcrystalline waxes, polyisobutene, polyvinylpyrrolidone/vinyl acetate copolymers, and insoluble polyacrylatecopolymers.

Also effective as adhesion enhancing agents are liquid hydrophilicpolymers including polyethylene glycols, nonionic polymers of ethyleneoxide having the general formula: HOCH₂ (CH₂OCH₂)_(n1)CH₂OH wherein n1represents the average number of oxyethylene groups. Polyethyleneglycols available from Dow Chemical are designated by a number such as200, 300, 400, 600, 2000 which represents the approximate averagemolecular weight of the polymer, as well as nonionic block copolymer ofethylene oxide and propylene oxide of the formula:HO(C₂H₄O)_(a1)(C₃H₆O)_(b1)(C₂H₄O)_(c1)H. The block copolymer ispreferably chosen (with respect to a1, b1 and c1) such that the ethyleneoxide constituent comprises from about 65 to about 75% by weight, of thecopolymer molecule and the copolymer has an average molecular weight offrom about 2,000 to about 15,000 with the copolymer being present in theliquid tooth whitening composition in such concentration that thecomposition is liquid at room temperatures.

A particularly desirable block copolymer for use in the practice of thepresent invention is available commercially from BASF and designatedPluraflo L1220 (PEG/PPG 116/66) which has an average molecular weight ofabout 9,800. The hydrophilic poly(ethylene oxide) block averages about65% by weight of the polymer.

Synthetic anionic polycarboxylates may also be used in the oralcompositions of the present invention as an efficacy enhancing agent forany antibacterial, antitartar or other active agent within thedentifrice composition. Such anionic polycarboxylates are generallyemployed in the form of their free acids or preferably partially or morepreferably fully neutralized water soluble alkali metal (e.g. potassiumand preferably sodium) or ammonium salts. Preferred are 1:4 to 4:1copolymers of maleic anhydride or acid with another polymerizableethylenically unsaturated monomer, preferably methylvinylether/maleicanhydride having a molecular weight (M.W.) of about 30,000 to about1,800,000 most preferably about 30,000 to about 700,000. Examples ofthese copolymers are available from GAF Corporation under the trade nameGANTREZ® (methylvinylether/maleic anhydride), e.g., AN 139 (M.W.500,000), AN 119 (M.W. 250,000); S-97 Pharmaceutical Grade (M.W.700,000), AN 169 (M.W. 1,200,000-1,800,000), and AN 179 (M.W. above1,800,000); wherein the preferred copolymer is S-97 Pharmaceutical Grade(M.W. 700,000).

When present, the anionic polycarboxylates is employed in amountseffective to achieve the desired enhancement of the efficacy of anyantibacterial, antitartar or other active agent within the oralcomposition. Generally, the anionic polycarboxylates is present withinthe oral composition from about 0.05% to about 4% by weight, preferablyfrom about 0.5% to about 2.5% by weight.

Adhesion enhancing agents employed in compositions of variousembodiments of the invention are present in an amount of from about 0 toabout 20% by weight. Preferably, the adhesion enhancing agents arepresent in an amount of from about 2 to about 15% by weight.

An embodiment of the composition optionally comprises a whitening agentwhich includes, but is not limited to peroxide compounds such ashydrogen peroxide, peroxides of alkali and alkaline earth metals,organic peroxy compounds, peroxy acids, pharmaceutically-acceptablesalts thereof, and mixtures thereof. Peroxides of alkali and alkalineearth metals include lithium peroxide, potassium peroxide, sodiumperoxide, magnesium peroxide, calcium peroxide, barium peroxide, andmixtures thereof. Organic peroxy compounds include carbamide peroxide(also known as urea hydrogen peroxide), glyceryl hydrogen peroxide,alkyl hydrogen peroxides, dialkyl peroxides, alkyl peroxy acids, peroxyesters, diacyl peroxides, benzoyl peroxide, and monoperoxyphthalate, andmixtures thereof. Peroxy acids and their salts include organic peroxyacids such as alkyl peroxy acids, and monoperoxyphthalate and mixturesthereof, as well as inorganic peroxy acid salts such as persulfate,dipersulfate, percarbonate, perphosphate, perborate and persilicatesalts of alkali and alkaline earth metals such as lithium, potassium,sodium, magnesium, calcium and barium, and mixtures thereof. In variousembodiments, the peroxide compound comprises hydrogen peroxide, ureaperoxide, sodium percarbonate and mixtures thereof.

In some embodiments a non-peroxide whitening agent may be provided.Whitening agents among those useful herein include non-peroxy compounds,such as chlorine dioxide, chlorites and hypochlorites. Chlorites andhypochlorites include those of alkali and alkaline earth metals such aslithium, potassium, sodium, magnesium, calcium and barium. Non-peroxidewhitening agents also include colorants, such as titanium dioxide andhydroxyapatite, pigments or dyes. In some embodiments the whiteningagent is separated from the aqueous carrier. In some embodiments thewhitening agent is separated from the aqueous carrier by encapsulationof the whitening agent.

In an additional aspect, the present invention provides a process formaking the core shell silica particles as defined above comprisingadmixing an amount of silica particles in water with an amount of abase, wherein the base comprises a group I metal ion, to produce thecore shell silica particles.

The base is not especially limited, provided it comprises a group Imetal ion. The base is typically a strong base. Preferably the base isselected from the group consisting of sodium hydroxide, potassiumhydroxide, sodium carbonate, potassium carbonate, trisodium phosphate,disodium phosphate, potassium phosphate, dipotassium phosphate,tetrasodium pyrophosphate, and tetrapotassium pyrophosphate. The basemay have a pKb value in the range 0.1 to 3. For example sodium hydroxidehas a pKb of 0.2, and potassium hydroxide has a pKb of 0.5.

In one embodiment of the composition, the composition comprises about65%-99.9% of the carrier and further included ingredients, i.e. one ormore of anti-caries agents, desensitizing agents, viscosity modifiers,diluents, surfactants, emulsifiers, foam modulators, pH modifyingagents, abrasives, mouth feel agents, sweetening agents, flavor agents,colorants, preservatives, amino acids, anti-oxidants, anti-calculusagents, a source of fluoride ions, thickeners, an active agent forprevention or treatment of a condition or disorder of hard or softtissue of the oral cavity, a whitening agent and combinations thereof.In another embodiment of the composition, the composition comprisesabout 80%-99.5% of the carrier and further included ingredients. Inanother embodiment of the composition, the composition comprises about90%-99% of the carrier and further included ingredients.

The description of the optional ingredients above is also intended toinclude any combination of ingredients.

Components for Forming CSS Particles

As mentioned above, the silica is preferably selected from the groupconsisting of a precipitated silica, a fumed silica and a fused silica.The silica may be synthetic amorphous precipitated silica, such asZeodent® 114 or Zeodent® 165 (J. M. Huber Corp), Absil 100 C or MFIL P(Madhu Silica). The silica may be a fumed silica, such as Aerosil 200(Evonik). In another embodiment, the silica is a fused silica, whichincludes but is not limited to CAB-O-SIL® HP-60, produced by CabotCorporation, TECO-SIL® 10 and TECO-SIL® 44css, produced by C-E Minerals,and Spheron P1500 made by the Japanese Glass Co.

Suitable silicas for use in the invention also include colloidal silicas(thickening silicas) having, such as the aerogels Syloid 244 and 266(available from W. R. Grace Company), Aerosil (available from DeGussaCo.) and pyrogenic silicas sold under the tradename Cab-O-Sils(available from Cabot Corporation). Tixosil 333 and Tixosil 43B(available from Rhodia Ltda.), Zeodent 165 (available from J. M. HuberCorporation).

Other suitable silicas for use in the invention include silica abrasiveswhich in turn include silica gels and precipitated amorphous silicas.These silicas are colloidal particles/particulates having an averageparticle size ranging from about 3 microns to about 12 microns, and morepreferably between about 5 to about 10 microns and a pH range from 4 to10 preferably 6 to 9 when measured as a 5% by weight slurry.Illustrative of silica abrasives useful in the practice of the presentinvention are marketed under the trade designation Sylodent XWA byDavison Chemical Division of W.R. Grace & Co., Baltimore, Md. 21203.Sylodent 650 XWA, a silica hydrogel composed of particulates ofcolloidal silica having a water content of 29% by weight averaging fromabout 7 to about 10 microns in diameter.

Other types of silica abrasives suitable for use in the inventioninclude precipitated silicas having a mean particle size of up to about20 microns, such as Zeodent 115, marketed by J.M. Huber ChemicalsDivision, Havre de Grace, Md. 21078, or Sylodent 783 marketed by DavisonChemical Division of W.R. Grace & Company.

The process may be carried out at a temperature in the range of from 17°C. to 90° C. In one embodiment the process is carried out at roomtemperature, i.e. 20 to 26° C. In another embodiment the process iscarried out at a temperature of from 70 to 90° C. When preparing thecore shell silica particles on an industrial scale, the mixer used tomix the reactants, such as a Lee mixer (Lee Industries), is preferablynot heated up.

In one embodiment the base is sodium hydroxide and the process iscarried out at a temperature of from 70 to 90° C. Preferably thetemperature is from 80 to 90° C. Preferably, the base is 50% aqueoussodium hydroxide solution.

In another embodiment the base is potassium hydroxide. When usingpotassium hydroxide the process may be carried out at room temperature.The use of potassium hydroxide is preferred because the higherreactivity of potassium hydroxide (as compared to sodium hydroxide)means that the need for heating is avoided, and the reaction can becarried out at room temperature. Room temperature. Room temperature,sometimes referred to as ambient temperature is typically from 20 to 26°C., and is the temperature achieved when no external heating of thereaction mixture is used. When preparing the core shell silica particleson an industrial scale, the mixer used to mix the reactants, such as aLee mixer (Lee Industries), cannot typically be heated up.

The reaction is:

2KOH+SiO₂⇒K₂SiO₃+H₂O

Typically, the formation of the core shell silica particles is completeafter a time period of 2 hrs.

The weight ratio of the amount of base (for example, 50% aqueous NaOHsolution) to the amount of silica particles is typically from 1:1 to1:20. In a preferred embodiment, the weight ratio for the amount of base(for example 50% NaOH) to the amount of silica particles is from 1:1 to1:6, optionally about 1:4. In one typical example 20% high cleaningsilica and 4.5% NaOH (50%) were used, and the ratio is 4.5%:20%=1:4.44).This ratio may be used for toothpaste compositions.

Typically, the turbidity of the core shell silica particles is reducedby increasing the weight ratio for the amount of base to the amount ofsilica particles. For transparent core-shell silica (CSS) the weightratio for the amount of base (for example 50% NaOH) to the amount ofsilica particles is greater than 0.5:1 and all of the silica particleshave been dissolved. For translucent CSS particles the weight ratio of50% NaOH to silica is from 0.45 to 0.49. For semi-opaque and opaque CSSparticles the weight ratio of 50% NaOH to silica is from 0.20 to 0.45.For typical CSS toothpaste compositions, a ratio of 1:4.44=0.225:1 isused.

In a preferred embodiment, the reaction of the silica particles with thebase causes a reduction in the d(0.5) value of the silica particles offrom 1 to 15 nm to form the silica core, and M₂SiO₃.xH₂O is formed ontop of the silica core. Typically, there is a greater reduction in thed(0.5) value of the silica particles as the weight ratio for the amountof base to the amount of silica particles increases (see Table 1).

TABLE 1 SiO₂/50% NaOH weight ratio Volume change How much V2 2.02 etchedaway X ΔV/V ΔY (nm) 20 −10.100% −1.31 18 −11.222% −1.46 16 −12.625%−1.64 14 −14.429% −1.87 12 −16.833% −2.19 10 −20.200% −2.62 9 −22.444%−2.91 8 −25.250% −3.28 7 −28.857% −3.75 6 −33.667% −4.37 5 −40.400%−5.25 4 −50.500% −6.56 3 −67.333% −8.74 2.02 −100.000%  −12.99Toothpaste 4.44  −45.45% −5.91

The reduction in the d(0.5) value of the silica particles of may be from1 nm to 6 nm. The amount of silica etched away depends on the BETspecific area of the silica particles. Particles with a greater surfacearea, e.g. porous particles like amorphous dental silica abrasives: highcleaning silica Zeodent 105; regular silica like Zeodent 114, thickeningsilica like Zeodent 165 will be etched less deep. Rigid silica particleswill have a greater depth of etching.

As the covalent bonds of the SiO₂ network are turned into ionic bondsbetween Na⁺ and SiO₃ ²⁻, the surface becomes polarized and adsorbs waterand the humectant to produce the core shell silica particle. As thereaction proceeds, the core shell silica particles can also become lesstransparent and more opaque, and the pH of the reaction solutiondecreases.

The weight ratio for the amount of humectant to water may be selectedfrom a group of ratios consisting of 4:1 to 1:4; 3:1 to 1:3; 2:1 to 1:2;and 5:3 to 3:5.

In one embodiment, the d(0.5) value of the core shell silica particlesformed by the process is at least 5% greater than the d(0.5) value ofthe silica starting material. It will be noted that although thediameter of the silica particle decreases during the process, forming asmaller silica core, the diameter of the whole CSS particle includingthe silicate layer is often greater than that of the original silicaparticle.

The formation of the core shell particles can be monitored bydetermining the pH of the reaction mixture. Core shell silica particlesare formed when the pH of the reaction mixture decreases by at least 0.5pH units from the initial mixture of reactants. Typically, the coreshell silica particles are formed when the pH of the reaction mixturedecreases by at least 0.8 pH units from the initial mixture ofreactants. In another embodiment, the end point of the process resultswhen pH of the reaction mixture decreases by at least 0.8-1.5 pH unitsfrom the initial mixture of reactants and does not exhibit any furtherdecrease in pH. The formation of the core shell silica particles isusually complete when the pH is about 11.

The formation of the core shell particles can also be monitored bydetermining the conductivity of the reaction mixture. The end point ofthe process results when the conductivity of the reaction mixturedecreases by at least 250 micro Siemens/cm (μS/cm) because the electriccharges transfer from highly mobile ions (NaOH) to much less mobilesilica surface (mobility≈0). In yet another embodiment, the end point ofthe process results when the conductivity of the reaction mixturedecreases by 250-400 μS/cm. Typically, the core shell silica particlesare formed when the conductivity of the reaction mixture decreases by atleast 2 milli Siemens/cm (mS/cm). Usually, the core shell silicaparticles are formed when the conductivity of the reaction mixturedecreases by at least 5 mS/cm.

Fumed Silica

Pyrogenic silica (sometimes called fumed silica or silica fume) is avery fine particulate or colloidal form of silicon dioxide. It isprepared by burning SiCl₄ in an oxygen rich hydrocarbon flame to producea “smoke” of SiO₂. The silica particles fuse with one another to formbranched, three-dimensional chain-like aggregates.

SiCl₄+2H₂+O₂→SiO₂+4HCl.

Precipitated Silica

Amorphous silica, silica gel, is produced by the acidification ofsolutions of sodium silicate. An initially formed gelatinous precipitateis then washed and then dehydrated to produce colorless microporoussilica. Idealized equation involving a trisilicate and sulfuric acid isshown:

Na₂Si₃O₇+H₂SO₄→3SiO₂+Na₂SO₄+H₂O

In the majority of silicates, the Si atom shows tetrahedralcoordination, with 4 oxygen atoms surrounding a central Si atom. Themost common example is seen in the quartz crystalline form of silicaSiO₂. In each of the most thermodynamically stable crystalline forms ofsilica, on average, all 4 of the vertices (or oxygen atoms) of the SiO₄tetrahedra are shared with others, yielding the net chemical formula:SiO₂. SiO₂ has a number of distinct crystalline forms (polymorphs) inaddition to amorphous forms. With the exception of stishovite andfibrous silica, all of the crystalline forms involve tetrahedral SiO₄units linked together by shared vertices in different arrangements.

Sodium Silicate

Sodium silicate is the common name for compounds with the formulaNa₂(SiO₂)_(n)O. A well-known member of this series is sodiummetasilicate, Na₂SiO₃. Also known as waterglass or liquid glass, thesematerials are available in aqueous solution and in solid form. Sodiumcarbonate and silicon dioxide react when molten to form sodium silicateand carbon dioxide:

Na₂CO₃+SiO₂→Na₂SiO₃+CO₂

Anhydrous sodium silicate contains a chain polymeric anion composed ofcorner shared {SiO₄} tetrahedral, and not a discrete SiO₃ ²⁻ ion. Inaddition to the anhydrous form, there are hydrates with the formulaNa₂SiO₃.nH₂O (where n=5, 6, 8, 9) which contain the discrete,approximately tetrahedral anion SiO₂(OH)₂ ²⁻ with water of hydration.For example, the commercially available sodium silicate pentahydrateNa₂SiO₃.5H₂O is formulated as Na₂SiO₂(OH)₂′4H₂O and the nonahydrateNa₂SiO₃.9H₂O is formulated as Na₂SiO₂(OH)₂.8H₂O.

In industry, the various grades of sodium silicate are characterized bytheir SiO₂:Na₂O weight ratio (weight ratios can be converted to molarratios by multiplication with 1.032), which can vary between 2:1 and3.75:1. Grades with this ratio below 2.85:1 are termed ‘alkaline’. Thosewith a higher SiO₂:Na₂O ratio are described as ‘neutral’.

In another embodiment, the silica is a precipitated silica, whichincludes, but is not limited to Zeodent® 114 and Zeodent® 165(precipitated silica particles produced by J.M. Huber—chemical name:synthetic amorphous silica), Sylodent® 783 produced by W.R. Grace,Sorbosil® AC-43 produced by Ineos (PQ Corp.)

In another embodiment, the silica is a fused silica, which includes butis not limited to CAB-O-SIL® HP-60, produced by Cabot Corporation,TECO-SIL® 10 and TECO-SIL® 44css, produced by C-E Minerals, and SpheronP1500 made by the Japanese Glass Co.

In one embodiment, sodium hydroxide reacts with the surface of the SiO₂particle to etch a shell of layers(s) of Na₂SiO₃ as follows:

SiO₂+2NaOH→Na₂SiO₃+H₂O

As can be seen from the reaction scheme, no NaOH will result in nochange to the silica, whereas at the other extreme, complete reactionwith 2 moles of NaOH per 1 mole of silica will result in the completeconversion into Na₂SiO₃. In order, to obtain the core shell particles ofthe invention, the reaction process must be controlled so as to notachieve particles comprising the appropriate proportion of Na₂SiO₃.

The core shell silica have adhesive properties when partially dried, forexample, by air-drying because hydrated Na₂SiO₃ is adhesive (waterglass).

In an embodiment, the core shell silica particles of the invention areformed when at least 1-6% of each of the silica particle startingmaterial has been etched with one or more monolayers of Na₂SiO₃. Inanother embodiment, the core shell silica particles of the invention areformed when at least 2.5-5% of each of the silica particle startingmaterial has been etched with one or more layers of Na₂SiO₃. In anotherembodiment, the core shell silica particles of the invention are formedwhen at least 3.5-4% of each of the silica particle starting materialhas been etched with one or more layers of Na₂SiO₃.

The formation of the core shell silica particles of the inventiondescribed above can be effected by manipulating the amount and type ofbase used, the amount of silica used, the amount of humectant used andvarying the temperature of the reaction.

In an embodiment, the process further comprises admixing silicaparticles and base with a humectant. In an embodiment, the processfurther comprises the weight ratio of the amount of humectant to theamount of water being between from 4:1 to 1:4. In an embodiment, theprocess further comprises the weight ratio of the amount of humectant tothe amount of water being from 3:1 to 1:3; from 2:1 to 1:2; or from 5:3to 3:5. In an embodiment, the humectant comprises a mixture of two ormore individual humectants. In an embodiment, the process furthercomprises a step of drying the product produced so as to remove aportion of the H₂O.

In an embodiment, the process further comprises reacting the amount ofSiO₂ particles with the amount of NaOH and humectant at 50° C. to 140°C. In an embodiment, the process further comprises reacting the amountof SiO₂ particles with the amount of NaOH at 70° C. to 100° C. In anembodiment, the process further comprises reacting the amount of SiO₂particles with the amount of NaOH at 70° C. to 90° C. In an embodiment,the process further comprises reacting the amount of SiO₂ particles withthe amount of NaOH at 70° C. to 80° C. In an embodiment, the processfurther comprises reacting the amount of SiO₂ particles with the amountof NaOH at 74° C. to 76° C. In an embodiment, the process furthercomprises reacting the amount of SiO₂ particles with the amount of NaOHat 75° C.

In general, the use of a humectant in the reaction process allows forthe use of higher temperatures within the ranges described above.

One of ordinary skill in the art can determine when the core shellsilica particles of the invention have been obtained by several means inaddition to sampling the reaction mixture and the test the core shellsilica particles formed until CSS particles with the requisiteproperties in terms of layer formation and charge density have beenformed.

In an embodiment, the end point of the process results when the averageparticle diameter of the core shell silica particle formed by theprocess is at least 5% greater in diameter than the average particlediameter of the silica (SiO₂) starting material. In another embodiment,the core shell silica particle is from 5%-10% greater in diameter thanthe average particle diameter of the silica starting material.

In an embodiment, the process further comprises admixing the core shellsilica particle produced with a carrier to make a composition. In anembodiment, the process further comprises adjusting the pH of thecomposition to achieve a value of 7-9 pH adjustment can be achievedusing an acid or base as necessary. In an embodiment, the pH adjustmentis achieved using an acid.

In an additional aspect, the present invention provides a core shellsilica particle obtainable by a process defined above.

In a further aspect, the present invention provides a method of reducingor inhibiting bacteria in the oral cavity which comprises applying theoral care composition defined above to a patient in need thereof to theoral surfaces of the patient.

In a final aspect, the present invention provides an ex vivo method ofreducing or inhibiting bacterial in a patient's removable oral devicewhich comprises applying the oral care composition described above tothe surface of the removable oral device. Preferably the removable oraldevice is a denture, tray, mouthpiece, orthodontial braces and aretainer.

Another embodiment of the invention is a method of using the core shellsilica particle for reducing or inhibiting bacteria in the oral cavityof a patient in need thereof, which comprises applying to the oralsurfaces of the patient the composition of the invention.

Another embodiment of the method for reducing or inhibiting bacteriacomprises applying the core shell silica particles ex vivo to a patientin need thereof, to the patient's removable oral device. In the contextof the invention, the removable oral device includes, but is not limitedto dentures, trays, mouthpieces, orthodontial braces and a retainer.

In one embodiment of the method, the patient is a mammal, whichincludes, but is not limited to humans and animals (e.g. dogs, cats,horses, cattle, sheep, llamas, etc.)

Another embodiment of the invention is the use of the core shell silicaparticle to make a composition for reducing or inhibiting bacteria inthe oral cavity of a patient in need thereof, which comprises applyingto the oral surfaces of the patient the composition of the invention orfor reducing or inhibiting bacteria comprises applying the core shellsilica particles ex vivo to a patient in need thereof, to a patient'sremovable oral device.

Embodiments of the present invention are further described in thefollowing examples. The examples are merely illustrative and do not inany way limit the scope of the invention as described and claimed.

EXAMPLES Example 1

The composition shown in Table 2 was used to produce the core shellsilica particles. Zeodent® 114 and Zeodent® 165 are precipitated silicaparticles produced by J.M. Huber (chemical name: synthetic amorphoussilica).

TABLE 2 Ingredients used in Example 1. Ingredients weight in gramsSorbitol 361.3 Water 43.8 Zeodent ® 114 40.8 Zeodent ® 165 40.2 SolidNaOH 4.0

Example 2

The core shell particles of the present invention were compared withother silica based particles. The compositions used are shown in Table3.

TABLE 3 Ingredients used in Example 2 Weight in grams Ingredient Control#1 Control #2 Example 2 Sorbitol 0 360 360 Water 483 43 43 Zeodent ® 11480 80 80 50% NaOH 0 0 8 Solid NaOH 4 0 0

Without wishing to be bound by theory, it was believed that theparticles produced in Control #1 did not have adhesive properties due tothe lack of humectant (e.g., sorbitol) to keep the water on the silicaparticles, a preferred condition to ionize SiO₂.

Without wishing to be bound by theory, the particles produced in Control#2 also did not have adhesive properties because there was no NaOH toconvert some of the SiO₂ into layers of Na₂SiO₃ covering the remainingSiO₂ core. In contrast, the core shell silica particles produced inExample 2 had adhesive properties similar to that of Example 1 above.These comparisons show that NaOH is needed, and water and/or humectantis/are preferable to obtain the core shell particles of the invention.

Example 3

In another comparative example, glycerin was substituted for sorbitol asthe humectant component, and in two different weight ratios to water.The compositions prepared are shown in Table 4. Control #3 is similar toExample 1, but uses glycerin instead of sorbitol as the humectant and 8g of 50% NaOH instead of 4 g of solid NaOH.

TABLE 4 Ingredients and Respective Weights Used in Control #3 andExample 3. Weight in grams Ingredient Control #3 Example 3 Glycerin361.3 252 Water 43.8 151 Zeodent ® 114 40.8 80 Zeodent ® 165 40.2 0 50%NaOH 8 8

Without wishing to be bound by theory, the particles produced in Control#3 did not have adhesive properties likely because there was aninsufficient amount of water to convert SiO₂ into Na₂SiO₃. In contrast,the core shell silica particles produced in Example 3 had adhesiveproperties.

Example 4

React SiO₂ abrasives with NaOH solution to create core-shell particles.

The reaction is: 2NaOH+SiO₂⇒Na₂SiO₃+H₂O

0.8% NaOH (50% solution) was used in clear silica colloids (see Table5). When NaOH reacts with excess SiO₂, the pH will go beyond 11, thencomes down gradually to below 10.0 (for toothpaste application, itrequires the pH range between 6 and 10). The transition time is 6-24hours at room temperature, but it may be much shorter by heating tohigher temperature such as 75° C. The optical properties of the colloidschange during the reaction, from transparent to opaque.

Table 5 making core-shell silica colloids (model colloids)

Core-shell silica colloids amount in grams Control amount in gramsSorbitol 359.8 Sorbitol 359.8 Water 43.2 Water 43.2 Zeodent 114 80Zeodent 114 80 mix for 30 minutes, clear colloids mix for 30 minutes,clear colloids 50% NaOH 8 Mix for several hours at room temperature,becomes semi-opaque

The optical appearance changes because the refractive index is changedon the shell. This makes sense because SiO₂ is known to be able to reactwith NaOH (or Na₂CO₃ or other strong bases) forming Na₂SiO₃, and therefractive index matched to SiO₂ (1.44-1.45) becomes mis-matched so thetransparency is gone.

The present inventors postulated that the product of NaOH+SiO₂ ishydrated Na₂SiO₃ (refractive index is lower than SiO₂, or n_(D)<1.44).To confirm this hypothesis, a higher refractive index non-crystallizingsorbitol (refractive index=1.455-1.465) was used to increase therefractive index of aqueous solution (surrounding silica particles) tomatch the refractive index of core shell silica. It does turn back intocompletely transparent colloids. This simple experiment evidences thatthe shell consists of low refractive index hydrated Na₂SiO₃ which isattached on the silica core. The inventors found a physical model forconcentric rigid non-porous spherical particle light scattering toexplain why colloids become opaque from transparent reactants.

Example 5 Physical Model for Core-Shell (Concentric) Particles LightScattering

This model is based on “light Scattering by Small Particles”, H. C. vande Hulst, 2003, pages 67-77.

The scattering intensity is proportional to the dielectric constant, α.

For simple spherical particles:

$\alpha = {\frac{m^{2} - 1}{m^{2} + 2} \times a^{3}}$

Where:

m=np/nm, where np and nm are the refractive indices of particle andwater aqueous medium surrounding the particles (water+sorbitol+salts)

a is the particle radius

For a concentric particle as shown in FIG. 1B:For the core particle, n1 is the refractive index, qa is the radius (qis the ratio of radius between core and shell).For the shell, n2 is the refractive index, a is the radiusWhere the refractive index (n) are defined as below:n=n1 for 0<r<qan=n2 for qa<r<an=1 for r>a (air for this case)The dielectric constant for such core-shell (concentric) particle is:(depends on only 4 parameters only: n1, n2, and q, a)

$\alpha = {a^{3} \times \frac{{\left( {n_{2}^{2} - 1} \right) \times \left( {n_{1}^{2} + {2n_{2}^{2}}} \right)} + {{q^{3}\left( {{2n_{2}^{2}} + 1} \right)} \times \left( {n_{1}^{2} - n_{2}^{2}} \right)}}{{\left( {n_{2}^{2} + 2} \right) \times \left( {n_{1}^{2} + {2n_{2}^{2}}} \right)} + {{q^{3}\left( {{2n_{2}^{2}} - 2} \right)} \times \left( {n_{1}^{2} - n_{2}^{2}} \right)}}}$

We can see the dielectric constant or light scattering intensity isdifferent for simple spherical and concentric particles.

Example 6

Plurality of monolayers: Calculations via ESCA, titration data, Ramanspectroscopy and mass indicate that the particle's shell comprisesmultiple monolayers of sodium silicates. Values of 2, 4, 16, 32 and 36shell monolayers were obtained.

ESCA Analysis of Core Shell Silica (CSS) Powder

ESCA (Electron Spectroscopy for Chemical Analysis) was used to determinethe surface composition of CSS powder, prepared in aqueous media fromSiO₂ and NaOH. ESCA only analyzes the outer 10 nm of the sample surface,so it the ideal method for detection of silicate on the surface of thesilica powder. The samples analyzed included the as dried powder as wellas that briefly rinsed three times with deionized water to remove anysoluble residues from the surface. The ESCA surface composition data forthe CSS powders are shown in Table 6.

TABLE 6 ESCA Analysis of Core Shell Silica (CSS) particles from SiO₂(Zeodent 105). Atomic percent O_(total) Si O_(SiO3) (O*) Na SiO₂(Zeodent 105) 69.30 30.30 0.00 0.41 Na-CSS (as dried) 65.17 29.53 2.223.13 3x H₂O rinse 65.94 29.24 1.94 2.52

The data reveal that a significant increase in sodium has occurred onthe surface of the as dried material, relative to that for silica. Inaddition, a low intensity oxygen peak that is characteristic of silicate(O_(SiO3)) was also observed in the data. This peak is not observed forSiO₂. The detection of Na and the silicate oxygen peak strongly supportthe formation of sodium silicate on the surface of the silica powder.Rinsing the as dried CSS powder with deionized water reduces the Na andsilicate oxygen slightly, indicating that the surface silicate has lowwater solubility. Thus the sodium silicate is largely retained on thesilica surface in aqueous media.

CSS powders that had been subjected to 1% CaCl₂ solution were alsostudied by ESCA to determine Ca uptake by the material. The ESCA resultsfor the as dried material clearly indicate the presence of Ca on thesurface of the CSS. A reduction in Na was also observed relative to theas dried CSS, suggesting that Ca substitutes for Na on the CSS surface.A low concentration of Cl was also detected for the CaCl₂ treated samplesuggesting residual CaCl₂ may also be present on the material. Deionizedwater rinsing of the sample removed the Cl, however most of the Ca wasretained. Thus the data indicate that the CSS is able to adsorb andretain Ca ions from aqueous solution. This result supports the Ca ionuptake data described above, and supports the potential for CSS to actas a tartar control agent.

Example 7

Mid IR and Polarization Analysis

Mid IR spectroscopy was used to confirm the presence of silicate presenton the shell layer of core silica. In all of the measurements, a three(multi) reflection ATR (Attenuated Total Reflectance) accessory was usedto enhance the absorption spectrum from the samples. These accessoriesonly allow light to penetrate 1-2 microns into the sample thus enhancingthe signal from surface components compare with the bulk matrix. Tofurther enhance the signal to noise, 32 scans were measured and averagedfor each measurement.

The Mid IR fingerprint of silica and silicate are quite different andwell resolved. Pure silica is characteristic of having a symmetric SiOvibration near 1074 cm-1 and a band around 960 cm⁻¹ due to thestretching vibration of SiOH bonds. Silicates, on the other hand, have aprominent asymmetric shoulder vibration between 1200 cm⁻¹ and 1100 cm⁻¹.In addition, a strong asymmetric stretch, shifted from silica is foundnear 1000 cm⁻¹.

The ATR spectral fingerprint of Core Shell Silica Paste is greatlyinfluenced by refractive index effects which can be large for inherentlystrong absorptions like Si—O stretching in silica and silicates. Intransmission the Si—O band is near 1100 cm⁻¹ but in ATR it is typicallyaround 1060 cm⁻¹. Also the bands are not totally symmetrical. Becausethese are pastes absorption is broad and potentially contains bothamorphous/crystalline material.

In addition to regular ATR measurements, a Polarization Accessory wasadded to enhance our understanding and confirmation that a surfacesilicate species was present. The benefit of polarization measurement isthat they give additional information on the molecular structure of asample as it pertains to the crystallinity or molecular orientation. Inthis application, as the plane of polarized light orients along thesample plane, the ratio of silica to silicate should change. Thepolarization angles tested were: 0, 30, 60, 90, 120, 150, and 180degrees. The spectral ratio of silicate (1022 cm⁻¹) to silica (1074cm⁻¹) were calculated to demonstrate presence of shell silicate. Table 7shows the results from this analysis for Na-CSS.

TABLE 7 Polarization Angle Ratio (degrees) Silicate/Silica 0 1.143 301.135 60 1.106 90 1.066 120 1.069 150 1.113 180 1.132

The analysis shows an optimal concentration of silicate at 0 degreeswhen the plane of polarized light is positioned suggesting that thedipole moment change of silicate is located horizontal to the ATRsurface.

Example 8 Kinetics

A kinetic study was conducted to determine the time period required tomake Na+-CSS colloids in situ. The following recipe was used based on aNa+-CSS toothpaste recipe (#85 CSS toothpaste).

TABLE 8 Na+-CSS colloid recipe Ingredients grams Water 1452 Glycerin2018 NaOH (50%) 270 Zeodent 105 1320

Procedure: add water, NaOH, and glycerin in a reaction container. AddZeodent 105 high cleaning silica slowly into the aqueous mixture. Heatup the mixture using a steam water-bath to maintain the reactiontemperature in the range of from 80-90° C. React for 6 hours. Take asample out every 1 hour to measure pH and conductivity when cooled downto room temperature. The data is listed below:

TABLE 9 Kinetic data conductivityt (micro time, hr Siemen/cm) pH 0 522012.218 1 1880 11.420 2 1324 11.508 3 1248 11.526 4 1077 11.544 5 68011.625 6 469 11.647

We can see from Table 9 that the pH and conductivity dramaticallydecrease in the first hour and then level out after 2 hours. Thereaction to form CSS reaction finishes in approximately 2 hours. Thiskinetic study is important because it is necessary to minimize thetoothpaste batch making time.

A potassium core shell silica (K-CSS) colloid based on the followingrecipe:

TABLE 10 K+-CSS colloid recipe Amount Ingredient in grams Water, 75° C.117 Glycerin 343 45% KOH 101.1 SiO₂ 220

Procedure: add hot water (75° C.), 45% KOH, and glycerin in a reactioncontainer. Add Zeodent 105 high cleaning silica slowly into the aqueousmixture. Let react for 6 hours at ambient temperature without additionalheating. Take samples out during the reaction to measure temperature, pHand conductivity. The kinetic data is listed below:

TABLE 11 Kinetic data for K+-CSS colloidal sample time conductivitytemperature (min) (μS/cm) (° C.) pH 0 9530 50.8 3 7520 51.9 4 6500 51.613 4240 46.6 11.107 21 3730 42.8 11.552 35 3290 37.6 11.552 46 3080 36.111.552 59 2888 33.2 11.566 75 2689 31 11.597 85 2465 29.9 11.606 2192291 25.7 410 2211 23.2 11.59

Table 11 shows that the conductivity dramatically decreases in the firsthour and then levels out after 2 hours. So the CSS reaction finishesafter approximately 2 hours at ambient (room) temperature.

The above colloid recipe was changed to make a K-CSS toothpaste bydecreasing the 45% KOH/SiO₂ from 101.1 g/220 g to 303.2 g/1321 g and didthe kinetic measurement again:

TABLE 12 K+-CSS colloid recipe (decreased KOH:SiO₂ ratio) AmountIngredient in grams Water, 75° C. 1005 Glycerin 2029.3 45% KOH 303.2SiO₂ 1321

TABLE 13 Kinetic data for #118 colloidal sample time conductivitytemperature (min) (μS/cm) (° C.) pH 0 (before adding 6.963 KOH) 934 0(after adding 49.6 11.66 KOH) 4530 1 3270 49.7 2 3030 49 3 2980 48.8 42910 48.3 5 2848 48 11.666 15 2684 44.6 11.568 29 2510 40.7 11.621 302462 40.9 11.572 40 2400 38.9 11.624 54 2282 36.7 11.634 79 2101 3311.646 92 2021 32.2 11.627 109 1970 30.7 11.649 115 1924 30.6 11.645From Table 13, we can see that the conductivity dramatically decreasesin the first half hour and levels out after 2 hours. Thus, K-CSScolloids for K-CSS toothpaste can be made in approximately 2 hours atambient temperature without any external heating (see K-CSS toothpastein Table 14). This kinetic study is important because it is necessary tominimize the toothpaste batch making time.

TABLE 14 K-CSS toothpaste Ingredient Amount in grams Thickener   0.2 PEG600 3 Humectant   37.305 Sweetener   0.5 Fluoride source    0.243 H₃PO₄2 45% KOH 5 (2.25% KOH) Zeodent 105 silica 20  Zeodent 165 silica   4.5Surfactant 2 Flavor   1.3 Water  23.7 FD&C #1 - blue dye    0.002 TiO₂coated mica   0.25 Total 100 The K-CSS toothpaste had a pH of 7.7 and a 10% pH of 8.06 (10% pH is thepH for 10% toothpaste solution by adding 10 g toothpaste in 90 g water(10% pH should be between 6 and 10 for toothpaste). Note that 1Brookfield viscosity unit is 10,000 centipoise.

ESCA spectroscopy was used to quantify the elements of K in the K-CSSparticle.

TABLE 15 ESCA data for K and Zn (2.25% KOH/2% H₃PO₄) in K-CSS toothpasteAtomic percent C O Na Si P K 4x H₂O wash 2.40 67.63 0.15 29.17 0.00 0.676x H₂O wash 2.03 67.82 0.13 29.45 0.00 0.58

We can see from Table 15 that K is found on the CSS abrasive surface. Insummary, KOH can be used as the base to make K-CSS toothpaste at roomtemperature.

Example 9

Process for Making K-CSS at Room Temperature

An example protocol for making K-CSS at room temperature is set outbelow:

Add pilot plant water at 75° C. to the lee mixer and then add glycerin.Add SiO2 (Zeodent 105). Add KOH. Mix ingredients. Remove samples atregular intervals and test pH and conductivity to determine whenformation of K-CSS is complete. Add H₃PO₄—the reaction mixture forms agel. Take sample out and add NaF, saccharin and water in the Lee mixer,and mix for 10 minutes. Disperse CMC/Xanthan gums in PEG 600 solution.Add the above gum solution in the Lee mixer. Mix. Slowly add Zeodent 165thickening silica. Apply 25 inch vacuum for a period of time. Removevacuum, and add flavor, dye, and mica. Turn on scraper and agitator, thecolor looks light blue, viscosity is quite thin before adding SLS. Mixfor 10 min under vacuum. Stop vacuum/mixing. Add SLS. Apply vacuum, mixslowly, to form a product which has a thicker consistency but is stillthin. The measured density of the final product is 1.279. The producthas a light blue colour. The measured initial viscosity=156600 cp after2 hrs sitting. Brookfield viscosity=150600 cp, barely flowable in a 1Gal jar.

Example 10

Transparent CSS

React SiO₂ abrasives with NaOH solution to create core-shell particlesat elevated temperature (70-90° C.). The reaction is:

2NaOH+nSiO₂⇒Na₂O-nSiO₃+H₂O  (1)

Previously, we made opaque toothpaste by reacting excess SiO₂ with NaOH(SiO₂:50% NaOH=20%:4.5%=4.44:1 weight percent ratio). In this way, onlya small portion (a surface) of the SiO₂ particle reacts with NaOH. Itwas not known how many percent of SiO₂ reacts with NaOH because theratio of SiO₂ to NaOH is n:2 based on the above reaction (n is notknown).

It was desirable to make transparent or translucent mouthwash productsusing CSS materials. It is necessary to know how much NaOH is needed tofully dissolve SiO₂ in order to make transparent CSS. We madetransparent CSS colloids from the following recipe by minimizing theratio of SiO₂ to 50% NaOH in order to achieve maximum particle chargedensity.

TABLE 16 Transparent Na-CSS colloids Ingredient Amount in grams molesWater 2847.4 Zeodent 105 280.1 4.662 50% NaOH 234 2.925

The SiO₂ was fully dissolved in NaOH at 85 C for 4 hours, formingtransparent liquid. When calculating their molar concentrations, themolar ratio of SiO₂ to NaOH (4.662 moles: 2.925 moles)=1.593:1 (molarratio). However, if we assume the following reaction:

2NaOH+SiO₂⇒Na₂SiO₃+H₂O  (2)

SiO₂: NaOH=1:2 molar ratio, only 2.925 moles/2 of SiO₂ dissolves, orDissolved SiO₂/total SiO₂=(2.925)/2 moles/(4.662 moles)=0.3138. Thus,the majority of SiO₂ is not dissolved. This is contradictory to what weobserved: all silica was apparently dissolved, forming transparentsolution. This calculation indicates that reaction (2) is invalid andreaction (1) is more appropriate. If all silica dissolved,n>2×1.593=3.186.

To further confirm this finding, 37.5% Na₂SiO₃ commercially availablefrom PQ Corp., was used as control sample in this study. For thiscommercial transparent Na2SiO3 liquid sample, SiO₂:Na₂O weightratio=3.220:1 or molar ratio=3.323:1. This is equivalent toSiO₂:NaOH=3.323:2=1.662:1. Na₂SiO₃/total SiO₂=(½) moles/(1.662moles)=30.08% Thus, for commercial Na₂SiO₃ solution, n>3.323.

The samples were analyzed by light scattering and ESCA to determine ifthere are some small nanometer particles in the transparent colloids.Based on the above recipe in Table 16, we fine-tuned the ratio of SiO₂to 50% NaOH and made the following recipes:

TABLE 17 Recipes for making opaque, translucent, and transparent Na-CSScolloids batch# #148 #149 #152 #153 #151 #150 Water (75° C.) 2867 28342824 2825 2826 2866 Zeodent 105 280 421 455 455 490 560 50% NaOH 234 224224 226.1 220 224 Ratio of Silica to 1.197 1.880 2.028 2.012 2.227 2.49750% NaOH pH 11.57 11.10 11.02 11.40 11.11 11.07 appearance transparenttransparent translucent translucent semi-opaque opaque mean particle 0 035.01 32.25 23.45 16.85 diameter, μmThe translucent Na-CSS colloid was found when SiO₂ to 50% NaOH weightratio=2.028:1 or molar ratio=2.700:1. So when n≤2.700×2=5.400, allsilica will fully dissolve. UV-visible spectra were measured for theabove 5 samples using a 0.20 mm thick quartz UV optical cell (see FIG.3). 14.6% Na2SiO3 solution, prepared from 37.5% Na₂SiO₃ commercialproduct from PQ Corp., was used as control sample.

It is seen that the translucent (#152) and transparent (#148 and #149)colloids have similar turbidity spectra as the control sample: there isno scattering in the visible region between 300 and 800 nm probablybecause of the absence of SiO₂ particles or if silica particles arepresent they are very small, and some scattering or absorption in the UVregion between 200 and 300 nm. As more silica is used in the formula,the semi-opaque (#151) and opaque (#150) samples show much higherscattering background from the SiO₂ particles in the visible and UVregions.

ESCA Analysis:

TABLE 18 ESCA Analysis of Na-CSS #152 Peak Position Atomic PercentAtomic Ratio (eV) O_(total) Si O_(SiO3) Na Si/O Na/Si Si #152 Na-CSS67.92 29.56 1.69 2.53 0.44 0.09 103.3 37.5% Na₂SiO₃ 63.56 23.25 11.7313.20 0.37 0.57 102.8 SiO₂ (Zeodent 114) 68.97 30.67 0.00 0.36 0.44 0.01103.4

Based on the above ESCA data, the translucent sample (#152) contains(based on Na data) Na₂SiO₃%=37.5%×2.53/13.20=7.19%. From the #152recipe, if all NaOH reacts with silica, we get 6.84% Na₂SiO₃, which isvery close to the value calculated from the above ESCA data (7.19%).

Table 19 below shows the particle size distributions for silica and CSSparticles as determined by light scattering. Table 19 shows the particlesize distribution for fumed silica, for an Na-CSS colloid, for Zeodent®105 precipitated silica, for an opaque Na-CSS (#150), for a semi-opaqueNa-CSS (#151), and for a translucent Na-CSS (#152).

TABLE 19 Composition d (0.1) d (0.5) d (0.9) Span (10%-90%) Fumed Silica20.08 μm 45.96 μm 92.75 μm 1.581 Zeodent 105  2.80 μm 10.31 μm 34.44 μm3.069 Silica #153 NaCSS 11.92 μm 28.78 μm 57.91 μm 1.598 Colloid # 150Colloids  4.62 μm 12.73 μm 34.67 μm 2.361 Na-CSS # 151 Colloids  8.07 μm19.85 μm 43.96 μm 1.808 # 152 Colloids 12.03 μm 31.29 μm 63.50 μm 1.645

The small particles may form bigger clusters due to the high surfacearea (energy). This was seen from the commercial fumed silica sample(mean particle diameter was reported to be 12 nm) which mean particlesize was 51.90 μm by a light scattering method. SEM picture alsorevealed that fumed silica particles form bigger clusters. It is seenfrom the particle size distributions: (1) the size distribution afterreaction with NaOH is narrower than the commercial Zeodent 105 highcleaning powder (control); (2) the smaller particles dissolve before thelarger size portion.

One other means to distinguish etched CSS particles from completelyformed metal silicate (e.g. Na₂SiO₃) is to compare viscosity. The 37.5%Na₂SiO₃ solidified at pH 11.3. When diluted nearly 10× to a 3.32%Na₂SiO₃, the solution still solidified at a pH of about 9. In contrast,the CSS particles of the invention remained in solution at theseconcentrations and pHs. As such, another embodiment of the invention isto form CSS particles which remain in a flowable colloidal form (i.e.non-solidified) over the entire 10% pH (pH for 10% toothpaste solutionby adding 10 g toothpaste in 90 g water) range of pH 6-10 which isdistinguishable from other completely formed metal silicates which wouldsolidify at pHs of about greater than or equal to pH 9.

Example 11

Etching of Silica by NaOH

CSS can be made from any kind of silica materials, e.g. rigid silicaparticles, porous silica particles like amorphous dental silicaabrasives: high cleaning silica Zeodent 105; regular silica like Zeodent114, thickening silica like Zeodent 165.

The amount of silica etched away depends on the BET specific area of thesilica particles—particles with a greater surface area will be etchedless deep. The amount of etching also depends on the ratio of silica tobase. It was found that when the weight ratio of Zeodent 105 silica vs50% NaOH solution=2.02 (endpoint), all silica dissolves. When we makeNa-CSS toothpaste, 20% high cleaning silica (Zeodent 105) and 4.5% of50% NaOH were used. So the ratio of SiO₂:50% NaOH=4.44:1. Sincedissolved SiO₂:50% NaOH=2.02:1, so the remaining SiO2 to NaOH(50%)=(4.44−2.02):1=2.42:1 after reaction. So the remaining SiO2 vsinitial SiO2=2.42/4.44=54.55%, or volume change(ΔV/V)=54.55%−100%=−45.45%. Note the endpoint for dissolving all silicamaterial might vary from SiO₂ to SiO₂ (different silicas may havedifferent endpoints, so for example endpoint for fumed silica may not be2.02:1).

Calculation from BET Specific Surface Area

Calculation for all SiO₂ (including both rigid and porous particles)uaing BET specific surface area (S/W). For high cleaning silica (e.g.Zeodent 105, S/W=35 m²/g and density d=2.2 g/cm³), the change inparticle diameter (ΔX) is given by the following formula:

ΔX=[(ΔV/V)/(S/W)]×1/d

ΔX=(−0.4545/35×10⁴ cm²/g)×(1/2.2 g/cm³)

ΔX=−5.90×10⁻⁷ cm

ΔX=−590 nm(−0.590 μm)

Calculation from Particle Diameter

An alternative calculation is available for monodisperse, rigid,spherical particles. Since the particle outer surface area is very small(compared to microporous particles), the rigid particles will have ahigher degree of etching.

Take the derivative:

$V = {\frac{1}{6}\pi \; D^{3}}$${dV} = {\frac{1}{2}\pi \; D^{2}{dD}}$$\frac{dV}{V} = {{3 \times \frac{dD}{D}} = {\frac{dD}{D} = {{- \frac{1}{3}} \times \frac{dV}{V}}}}$

For a 12 nm fumed silica (e.g. Aeorsil 200), if dV/V=−0.4545 by assumingthe same relative volume change ratio as high cleaning silica (e.g.Zeodent 105), the change in particle diameter ΔD=−0.1515×12 nm=−1.8 nm.This change in diameter (−1.8 nm from a 12 nm silica) is proportionallygreater than the high cleaning silica (−0.590 μm of a 10 μmsilica=5.9%).

Example 12

Model for the Number of Layers of Na₂SiO₃ on Silica Surface Using ESCAData

ESCA (Electron Sprectroscopy for Chemical Analysis—also known as XPS orX-ray Photelectron spectroscopy) can penetrate down from surface to 10nm deep. 1 layer of Silica or Na2SiO₃ is ca. 1 Å (0.1 nm). For Na₂SiO₃molecule: Na/Si=2:1. So for 100 monolayers, Na/Si=0.02:1. But from ESCAdata: Na/Si=0.084:1 So there are 0.084/0.02=4.2=4 layers of Na2SiO₃.

Example 13

Model for the Number of Layers of Na₂SiO₃ on Silica Surface Using RamanSpectroscopy

${B\; 1} = {\frac{{Na}\; 2{SiO}\; 3\mspace{14mu} {weight}\mspace{14mu} (g)}{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {total}\mspace{14mu} {weight}\mspace{14mu} (g)} \times 100\% \mspace{14mu} \left( {{determined}\mspace{14mu} {by}\mspace{14mu} {Raman}\mspace{14mu} {Spectroscopy}} \right)}$${B\; 2} = {\frac{\mspace{11mu} {{Na}\; 2{SiO}\; 3\mspace{14mu} {weight}\mspace{14mu} (g)}}{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)} = {{\frac{{Na}\; 2{SiO}\; 3\mspace{14mu} {weight}\mspace{14mu} (g)}{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {weight}\mspace{14mu} (g)} \times \frac{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {weight}\mspace{14mu} (g)}{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)}} = {B\; 1 \times {CSS}\mspace{14mu} {colloid}\mspace{14mu} {density}\mspace{14mu} (d)}}}$${B\; 3} = {\frac{{Na}\; 2{SiO}\; 3\mspace{14mu} {weight}\mspace{14mu} (g)}{{Silica}\mspace{14mu} {surface}\mspace{14mu} \left( {cm}^{2} \right)} = {\frac{{Na}\; 2{SiO}\; 3\mspace{20mu} {weight}\mspace{14mu} (g)}{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)} \times \frac{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)}{{Silica}\mspace{14mu} {surface}\mspace{14mu} \left( {cm}^{2} \right)} \times \frac{{Silica}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)}{{Silica}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)}}}$  where:$\mspace{20mu} {\frac{{Silica}\mspace{14mu} {surface}\mspace{14mu} \left( {cm}^{2} \right)}{{Silica}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)} = {\frac{4\pi \; r^{2}}{\frac{4}{3}\pi \; r^{3}} = \frac{3}{r}}}$$\frac{{Silica}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)}{{CSS}\mspace{14mu} {colloid}\mspace{14mu} {volume}\mspace{14mu} \left( {cm}^{3} \right)} = {{silica}\mspace{14mu} {volume}\mspace{14mu} \% \mspace{14mu} \left( {\Phi \mspace{14mu} \%} \right)\mspace{14mu} {determined}\mspace{14mu} {from}\mspace{14mu} {CSS}\mspace{14mu} {recipe}}$$\mspace{20mu} {{B\; 3} = {{B\; 2 \times \frac{r}{3} \times \frac{1}{\Phi \mspace{14mu} \%}} = {B\; 1 \times d \times \frac{1}{3} \times \frac{r}{\Phi \mspace{14mu} \%}}}}$${B\; 4} = {\frac{\# \mspace{14mu} {of}\mspace{14mu} {Na}\; 2{SiO}\; 3\mspace{14mu} {molecules}}{{Silica}\mspace{14mu} {Surface}\mspace{14mu} {area}\mspace{14mu} \left( {cm}^{2} \right)} = {\frac{B\; 3}{{Na}\; 2{SiO}\; 3\mspace{11mu} {M.W.}} \times 6.023 \times 10^{23}}}$$\begin{matrix}{{B\; 5} = {{Na}\; 2{SiO}\; 3\mspace{14mu} {surface}\mspace{14mu} {coverage}\mspace{14mu} (\theta)}} \\{= \frac{\# \mspace{14mu} {of}\mspace{14mu} {Na}\; 2{SiO}\; 3\mspace{14mu} {molecules}}{\# \mspace{14mu} {of}\mspace{14mu} {SiO2}\mspace{14mu} {molecules}}} \\{= \frac{B\; 4}{\left( \frac{\left( {1\mspace{14mu} {cm} \times 10^{8}A\text{/}{cm}} \right)^{2}}{{SiO2}\mspace{14mu} {molecule}\mspace{14mu} {cross}\mspace{14mu} {section}\mspace{14mu} {area}\mspace{14mu} \left( A^{2} \right)} \right)}} \\{= {\frac{B\; 1 \times d \times \frac{1}{3} \times \frac{r}{\Phi \mspace{14mu} \%}}{{Na}\; 2{SiO}\; 3\mspace{11mu} {M.W.}} \times}} \\{\frac{6.023 \times 10^{23}}{\left( \frac{\left( {1\mspace{11mu} {cm} \times 10^{8}A\text{/}{cm}} \right)^{2}}{{SiO2}\mspace{14mu} {molecule}\mspace{14mu} {cross}\mspace{14mu} {section}\mspace{14mu} {area}\mspace{14mu} \left( A^{2} \right)} \right)}} \\{= {\frac{3.5\% \times 1.189 \times \frac{5 \times 10^{- 4}{cm}}{3 \times 8.13\%}}{122.06} \times}} \\{\frac{6.023 \times 10^{23}}{\left( \frac{\left( {1\mspace{14mu} {cm} \times 10^{8}A\text{/}{cm}} \right)^{2}}{0.762\mspace{14mu} A^{2}} \right)}} \\{= {32.1\mspace{14mu} {layers}}}\end{matrix}$

Example 14

Spray Dry Synthesis of CSS Particles

Synthesis Procedure:

Add water and 50% NaOH in a reaction container. Keep stirring with amechanical stirrer (ca.200 RPM). Heat up the aqueous solution using 100°C. steam water-bath to control the temperature at 80-90° C. Add Zeodent105 (high cleaning silica powder) into the solution slowly. Keepstirring. react for 4 hours to make Na+-CSS colloids at ca. 85° C. Stopheating and cool down to room temperature. Keep stirring overnight. Usefilter paper to filter the above colloids with vacuum. Collect thefiltered liquid. Wash the Na+-CSS wet solid using water to remove thesoluble metal ions. Dry the Na+-CSS colloid to obtain dry Na-CSSabrasive by spray drying. Calculate yield (close to 100%), which yieldwas slightly over 100% because there were some water moisture in thesolid without complete evaporation during drying.

Example 15

Freeze Dry Procedure

Alternatively, the filtered liquid of Example 14 is then mixed with DIwater, the mass ratio between water and Na-CSS is about 1:1. Freeze themixture until it becomes solid. Turn on the freeze drier to cool thechamber. When the temperature of the chamber drops down to −47° C., loadthe frozen sample into the chamber and turn on vacuum for a period oftime sufficient to form dried CSS powder.

Example 16

The core shell silica (CSS) particles of the invention were testing foranti-bacterial activity using the resazurin anti-bacterial test assaywherein the reduction of resazurin is a measure of reduction ofbacterial growth.

All solutions are measured for the bacterial viability using resazurinmicroassay with Chemostat Inoculum (bacteria cocktail with A. viscosus,S. oralis, V. parvula, L. casei, and F. nucleatum) used in oral careproduct evaluation. Resazurin (7-Hydroxy-3H-phenoxazin-3-one 10-oxide)is a blue dye used as oxidation-reduction reaction, quantifies bacterialviability from color perception with respiring reaction effect.

Each experiment is conducted with live and dead bacterial cocktail withA. viscosus, S. oralis, V. parvula, L. casei, and F. nucleatum using TSBbroth (trypticase soy broth) and ethanol respectively and they wereadded at proper ratio to generate standard curve from 100% livebacterial cocktail to 100% dead bacterial cocktail collecting at a totalof 12 points.

The assay is performed using bacteria pellet from 1 ml ChemostatInoculum and exposed with ¼ strength trypticase soy broth: test solutionat 1:1 ratio in Eppendorf tube. After 1 hr incubation further bacteriagrowth was deactivated adding 1 ml D/E Broth with proper mixing andcollected pellet was rinsed with 1 ml TSB broth to remove D/E brothcompletely (D/E=Dey-Engley). The last pellet was resuspended in 1.5 mlTSB broth & 100 μL amount was transfer in to 96 well plate with 100 μLof resazurin dye solution in 96 well plate. OD measurement was done withresazurin assay protocol after 3-5 min incubation at 37° C. to achieveperfect dye reaction.

The microassay is conducted once a day for 4-5 days considering thedifferences in bacteria from biology aspect from day to day. Final %bacterial viability represents average value. Present ingredientsconcentration is set to actual concentration in the Toothpaste formula.

TABLE 20 Resazurin anti-bacterial test (viability level) % of viableTest compositions bacteria Positive control (1% ZnCl₂ + water) 4.88Na-CSS 2.34

As can be seen from the data in Table 20, the core shell silicaparticles provide higher anti-bacterial activity than zinc chloride(ZnCl₂), a known anti-bacterial agent.

As those skilled in the art will appreciate, numerous changes andmodifications may be made to the embodiments described herein withoutdeparting from the spirit of the invention. It is intended that all suchvariations fall within the scope of the appended claims.

1-56. (canceled)
 57. An oral care composition comprising core shell silica particles and an orally acceptable carrier, wherein each core shell silica particle comprises a silica core, and a group I metal silicate formed on top of the silica core.
 58. The oral care composition according to claim 57, wherein the metal silicate comprises the formula M₂SiO₃.xH₂O, wherein M is a group I metal, and x is from 0 to 10, optionally wherein M is Na or K.
 59. The oral care composition according to claim 57, wherein the outer 10 nm depth of each particle comprises from 0.1 to 10 weight % M₂SiO₃.xH₂O.
 60. The oral care composition according to claim 57, wherein the outer 10 nm depth of each particle has the general formula: (SiO₂)_(p)[O_(o)*M⁺ _(m)H⁺ _(h)OH⁻ _(j)].qH₂O wherein O* is oxygen in the silicate form; M is a group I metal ion; p, o, m, h, j and q are the atomic percentages of each component; and the total charge of each core shell silica particle is zero.
 61. The oral care composition according to claim 57, wherein the outer 10 nm depth of each particle has one of the following compositions: (SiO₂)_(30.30)Na_(0.41).8.70H₂O (SiO₂)_(30.67)Na_(0.36).7.63H₂O (SiO₂)_(23.25)[O*_(11.73)H_(10.26)Na_(13.20)].5.33H₂O
 62. The oral care composition according to claim 57, wherein the d(0.5) value of the particles is from 5 nm to 50 μm, from 26 μm to 40 μm, 18 μm to 25 μm, from 10 μm to 15 μm or from 5 nm to 12 nm.
 63. The oral care composition according to claim 57, wherein the M₂SiO₃.xH₂O comprises a plurality of monolayers of M₂SiO₃.xH₂O, optionally wherein the number of monolayers is from 2 to 100, 2 to 40, 2 to 12 or 12 to 40 layers.
 64. The oral care composition according to claim 57, wherein the silica is selected from the group consisting of a precipitated silica, a fumed silica and a fused silica.
 65. The oral care composition according to claim 57, wherein the core shell silica particles have a total cationic ion exchange capacity of from 0.5 to 5.0 meq/g.
 66. The oral care composition according to claim 57, wherein the oral care composition is in the form of a solid, paste, gel composition or liquid composition.
 67. The oral care composition according to claim 57, wherein the orally acceptable carrier further comprises a humectant.
 68. The oral care composition according to claim 57, wherein the composition further includes anti-caries agents, desensitizing agents, viscosity modifiers, diluents, surfactants, emulsifiers, foam modulators, pH modifying agents, abrasives, mouth feel agents, sweetening agents, flavor agents, colorants, preservatives, amino acids, anti-oxidants, anti-calculus agents, a source of fluoride ions, thickeners, an active agent for prevention or treatment of a condition or disorder of hard or soft tissue of the oral cavity, an adhesive agent, a whitening agent and combinations thereof.
 69. A method for reducing or inhibiting bacteria in the oral cavity comprising: administering an oral care composition according to claim 57 to an oral surface of a patient in need thereof. 